The present invention relates to the encapsulation of hybrid circuits in a package. It relates, more particularly, to a method of wiring between outputs of the package and constituent elements of the hybrid circuit, namely screen-printed tracks, passive components or semiconductor components for example. It can be applied notably to power hybrid circuits where the wiring at the package outputs calls for large-sectioned wires. It can be applied more particularly to power electronics applications that are subject to constraints of limited availability of space, as in the automobile, aeronautical and space sectors.
The metal packages designed for power hybrid circuits are deep. This complicates the wiring in the vicinity of the edges of the package and, more particularly, at the outputs. Besides, for reasons of reliability, the connection wires between the outputs and the elements to be wired should follow a certain radius of curvature that is sufficiently large. This constraint introduces a loss of space at the edges of the package. This loss is further accentuated by the fact that a connection zone is needed between the outputs of the package and the components, notably in the case of ultrasonic soldering, for reasons of compatibility among materials. Ultrasonic soldering is used because it is easy to implement, particularly in that the use of soldering irons is avoided.
These problems are further complicated by the circulation of the strong currents which, in certain cases, dictate a great increase in the number of connection wires. Finally, in the case of packages with small surface areas such as packages of the TO254 type manufactured by the firm XERAM for example, these problems become acute and jeopardize the manufacture of the hybrid circuits.
However, several approaches can be used to resolve these problems. A first approach consists in replacing the large-sectioned connection wire by several smaller-sectioned wires which can tolerate a smaller radius of curvature. However, the size of the connection zones limits the number of these wires and the space gained is not sufficient. Furthermore, the wiring of several wires in parallel increases manufacturing costs. A second approach enables the elimination of the connection zone, hence provides a gain in surface area since the connection wire is wired directly between the output of the package and the component or its receiving zone which is generally made of gold-platinum. Nevertheless, in this case, it is not possible to carry out the soldering operations by ultrasonic means. For, this method calls for gold surfaces. It is therefore necesssary to resort to a standard type of soldering. Now, the height of the package prevents the introduction of the soldering iron in the vicinity of the edges and even prevents the soldering when the packages have an excessively small surface area. In fact, in order to keep within the dictated availability of space, the current approach consists in using aluminium connection wires, having a diameter that is sufficient for the currents brought into play, with very small radii of curvature, at the limits of reliability. It is difficult to shape these wires. The wirings thus made are then tested in order to show up the ones that are defective. The yield obtained is clearly very poor. Besides, this method calls for two operations of deposition, one of gold for the wiring and the other of gold-platinum for the soldering of the ceramic substrates and components.
This method therefore calls for an operation for the mounting of the hybrid circuit by soldering and then a wiring operation carried out by specific and costly machines.
The aim of the invention is to overcome the above-mentioned drawbacks.